The Government last week officially declared Northland was in drought. WeatherWatch.co.nz said Gisborne and Hawke's Bay also had drought conditions.
"But the rain expected this week will likely linger in the Gisborne area in particular," Duncan said.
Duncan said Hawke's Bay and Wairarapa will get a mix of drizzle and downpours overnight tonight which are likely to intensify as the rain clouds move into the Gisborne area.
The Coromandel will also get a smattering of rain.
"It's an unusual set-up with a wet southeast flow across the upper North Island for Thursday.
"This means Gisborne, western Bay of Plenty, eastern Coromandel Peninsula and eastern Northland are all candidates for rain this week. As for totals - they will be incredibly varied due to the patchy nature of the rain clouds plus our large mountains/ranges - but we may be seeing 20 to 40mm of rain falling in a number of areas. Gisborne City may receive 30 to 40mm."
Duncan said although the rain set to fall in Northland wouldn't be enough to reverse the drought, it would put more of a dent in the dry conditions in Gisborne.
"Hawke's Bay, being on the fringes, may be disappointed with how much falls - but there is still potential for some heavier downpours, especially in the north of the region."
Meanwhile, the end of the long weekend spelled the end of the golden weather with cloud and warm, muggy temperatures and drizzle and rain around much of the North Island today, and fog in Wellington this morning.
Although Gisborne and Hawke's Bay will each reach about 34C today, that will drop dramatically to late teens tomorrow thanks to a southerly change.
The southerly has already affected parts of inland Southland and Otago, which tonight will get closer to freezing than double digits.
"Dunedin's high on Wednesday is just 14C and it may even struggle to reach that. A cool night tonight in the lower South Island and a cooler couple of days coming up for the sweltering east coast of the North Island."
The rest of the week will remain cool in the east until Sunday when it will get up to around 30C again.
The South Island may not experience a proper summer until the second half of February, Duncan said.
The MetService says Northland, Auckland, Coromandel and Bay of Plenty will be cloudy today and get scattered showers tomorrow, possibly becoming heavy around Tauranga.
Waikato, Waitomo and the central high country will experience drizzle but it will turn to rain tonight before clearing briefly tomorrow morning and getting heavy again later in the day.
The rain will hit the eastern and western coasts this afternoon - from Taranaki to Wellington, and Gisborne to Wairarapa - with heavy falls tomorrow.
The South Island has increasing fine periods, with high cloud and late rain in Fiordland on Thursday.
